The invention relates to an assisted hydraulic braking system designed especially to be used on a motor vehicle.
On vehicles equipped with an assisted hydraulic braking system, this system conventionally comprises a booster and a master cylinder which are arranged end to end. More specifically, the brake pedal acts on a control rod of the booster, the effect of this being to actuate, within the latter, boosting means moving a push rod which in turn actuates at least one actuating piston equipping the master cylinder. This compact arrangement is advantageous, because it makes it possible to give the booster/master-cylinder assembly a relatively simple structure.
However, there are circumstances in which it is not possible to place the booster directly between the brake pedal and the master cylinder. This situation arises particularly on some vehicles with right-hand drive. In fact, the diametral bulk of the booster can then make it impossible to install it directly between the brake pedal and master cylinder.
FR-A-2 629 033 discloses an assisted hydraulic braking system comprising a brake pedal, a master cylinder, a brake booster and at least one wheel brake, the master cylinder comprising a body equipped with a bore, in which at least one piston for actuating the wheel brake slides sealingly, and the booster comprising a control rod actuating boosting means acting on a push rod which actuates the piston of a hydraulic pressure transmitter, characterized in that the brake pedal acts on an actuating rod of the master cylinder, a first hydraulic circuit putting a control chamber of the master cylinder, formed between the actuating rod and the actuating piston, in communication with a control chamber of the booster, partially delimited by the control rod, in such a way that an actuation of the brake pedal causes a movement of the control rod with the effect of actuating the boosting means, and a second hydraulic circuit putting an actuating chamber of the booster in communication with an actuating chamber of the master cylinder, partially delimited by the actuating piston, in such a way that a movement of the push rod controlled by the boosting means causes a movement of the actuating piston with the effect of actuating the brake.
In a braking system so designed, the brake pedal is placed in the extension of the master cylinder, while the booster can be placed at any location under the bonnet of the vehicle. In fact, the pressure increase arising as a result of the actuation of the brake pedal is transmitted to the booster by the first hydraulic circuit, and the boosting force generated by this booster is in turn transmitted to the master cylinder by the second hydraulic circuit, whatever the position occupied by the booster in relation to the master cylinder.
However, such a system can have some disadvantages. In fact, the booster and the master cylinder are distant from one another and are connected to one another by means of hydraulic pipelines. During the actuation of the brake pedal, the hydraulic fluid contained in these pipelines is subjected to a high pressure. The large number of hydraulic connections under pressure, which is provided in this design, causes a proportionate increase in the risk of leaks.
Furthermore, the special design of the master cylinder intended for equipping such a braking system implies an increase in the number of its components, of the sealing sliding actions and of the return springs. The result of this, therefore, is that it is necessary to exert on the brake pedal a force higher than that which has to be exerted on the brake pedal of a conventional system, and this is contrary to the intended purpose of assisting the braking operations.